reset 
set data style lines  
set nokey
set xrange [0:30]
set xtics 1
set yrange [0:8]
set ytics 1
set grid
S0(x) = 4.1 + (0.748582)*(x - (27.7)) + (0)*(x - (27.7))**2 + (-0.910165)*(x - (27.7))**3
S1(x) = 4.3 + (0.502837)*(x - (28)) + (-0.819149)*(x - (28))**2 + (0.116312)*(x - (28))**3
S2(x) = 4.1 + (-0.786525)*(x - (29)) + (-0.470213)*(x - (29))**2 + (0.156738)*(x - (29))**3
Sp0(x) = ( x >= 27.6 && x <= 28.1) ? S0(x) : 0/0
Sp1(x) = ( x >= 27.9 && x <= 29.1) ? S1(x) : 0/0
Sp2(x) = ( x >= 28.9 && x <= 30.1) ? S2(x) : 0/0
plot 'pontos.txt' using 1:2 t 'pontos' with points pt(7) lt(8)
replot Sp0(x)
replot Sp1(x)
replot Sp2(x)
pause -1  
set out 'splineCubicaMono.eps' 
set term post mono 'Times-Roman' 18 
replot